[erlang-questions] Distributed Erlang ... alternate port?

Mike Berrow mberrow1@REDACTED
Mon Mar 17 02:49:17 CET 2008

>> Is there a way to run distributed erlang through an alternate port ?
>> [...]
>>  I know erlang needs both TCP and UDP on port 4369 normally.
>>  Is there any way to configure it to use other ports?
> Yes, but there are two different TCP ports you should be aware of.
> First is epmd, which is what listens on 4369.  This number is hard
> coded into the Erlang binaries.  It looks like you can change the
> definition of EPMD_PORT_NO in erts/epmd/epmd.mk, but I've never played
> with this.
> Second is erlang's distribution code, which uses the kernel
> application's inet_dist_listen_min and inet_dist_listen_max to decide
> what TCP port to listen on.  After creating a listening socket, it
> registers this port with epmd.

Hmmm.  So, at the remote node, epmd will be listening on 4369.  I was hoping
that I could get erlang on the local machine to believe it could connect
to an apparently  "local" erlang epmd on a different port (the local ends of the tunnels I make).
But if that is hard coded on both ends, I guess I am out of luck without going to
some very custom build. That would be a pity.
The "inet_dist_listen_min and inet_dist_listen_max" also indicates that there are even other
ports coming into play that I would need to re-map.

A use case example I can offer is monitoring and control of many, geographically dispersed
remote weather stations. The access restriction is that I can only get in (practically) through
the ssh port (22). There is no opening of extra ports through firewalls.
That's the motivation for the tunneling approach.

-- Mike Berrow

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